Rubber composition

ABSTRACT

The present invention provides a rubber composition comprising 100 parts by weight of a diene rubber component, 10 to 200 parts by weight of a reinforcing agent, and 0.1 to 15 parts by weight of a fatty acid salt. For example, the diene rubber preferably comprises a diene rubber having a heteroatom-containing polar group, the reinforcing agent preferably comprises carbon black or silica, and the fatty acid salt preferably comprises a metal salt of a C 5  to C 36  fatty acid. This rubber composition yields a vulcanized rubber showing improvements in heat build-up, tensile strength, abrasion resistance and processability.

TECHNICAL FIELD

This invention relates to rubber compositions which yield vulcanizedrubbers showing improvements in heat build-up, tensile strength,abrasion resistance and processability.

BACKGROUND ART

In recent years, as growing importance is attached to resource savingand environmental protection, the demand for a reduction in the fuelconsumption of automobiles has become increasingly stronger. Also forautomobile tires, it is desired to reduce their rolling resistance andthereby contribute to a reduction in fuel consumption. In order toreduce the rolling resistance of tires, it is common practice to use, asthe rubber material for tires, a rubber material which can yield avulcanized rubber showing a low degree of heat build-up.

Conventionally, it has been proposed to reduce heat build-up by using,as the rubber material for tires, a rubber composition comprising adiene rubber into which, in place of carbon black, silica isincorporated as a reinforcing agent. However, as compared with carbonblack-filled rubber compositions, such silica-filled rubber compositionshave the disadvantage that they fail to achieve sufficient abrasionresistance and tensile strength. One of the causes therefor is believedto be that silica has a lower affinity for diene rubbers than carbonblack and hence fails to exhibit a sufficient reinforcing effect.

Conventionally, a method for enhancing the affinity of silica for dienerubbers by using a silane coupling agent has been proposed (JapanesePatent Laid-Open No. 252431/'91. Japanese Patent Laid-Open No.252433/'91, etc.). However, in order to achieve a satisfactory effect,this method requires the use of a large amount of an expensive silanecoupling agent.

As another improvement, the use of a diene rubber into which asubstituent group having an affinity for silica has been introduced isbeing investigated. For example, diene rubbers having a tertiary aminogroup introduced thereinto (Japanese Patent Laid-Open No. 101344/'89)have been proposed for diene rubbers formed by emulsion polymerization;and diene rubbers having introduced thereinto an alkylsilyl group(Japanese Patent Laid-Open No. 188501/'89), a halogenated silyl group(Japanese Patent Laid-Open No. 230286/'93) or a substituted amino group(Japanese Patent Laid-Open No. 22940/'89) have been proposed for dienerubbers formed by anionic polymerization.

However, most of the diene rubbers having the aforesaid substituentgroups introduced thereinto show poor processability because, when theyare mixed with silica, they cohere strongly with silica and cannot bedispersed satisfactorily. Moreover, they also have the disadvantage thattheir properties such as heat build-up, tensile strength and abrasionresistance are not fully improved.

An object of the present invention is to provide a rubber compositioncontaining a diene rubber component and a reinforcing agent, and capableof yielding a vulcanized rubber which shows a low degree of heatbuild-up, exhibits excellent tensile strength and abrasion resistance,and has good processability.

DISCLOSURE OF INVENTION

The present inventors have made intensive investigations with a view toovercoming the above-describe problems of the prior art. As a result, ithas now been discovered that a composition obtained by incorporating afatty acid salt (e.g., calcium stearate) into a mixture of a dienerubber and a reinforcing agent can yield a vulcanized rubber showingimprovements in heat build-up, tensile strength, abrasion resistance andprocessability. The present invention has been completed on the basis ofthis discovery.

Thus, the present invention provides a rubber composition comprising 100parts by weight of a diene rubber component, 10 to 200 parts by weightof a reinforcing agent, and 0.1 to 15 parts by weight of a fatty acidsalt.

Diene Rubber Component

No particular limitation is placed on the type of the diene rubbercomponent used in the present invention, provided that it is arubber-like polymer formed chiefly from a conjugated diene. Specificexamples thereof include natural rubber (NR), polyisoprene rubber (IR),emulsion-polymerized styrene-butadiene copolymer rubber (SBR),solution-polymerized random SBR (containing 5 to 50% by weight of boundstyrene and having a 1,2-linkage content of 10 to 80% in the portionsconsisting of combined butadiene units), high-trans SBR (having atrans-form content of 70 to 95% in the portions consisting of combinedbutadiene units), low-cis polybutadiene rubber (BR), high-cis BR,high-trans BR (having a trans-form content of 70 to 95% in the portionsconsisting of combined butadiene units), styrene-isoprene copolymerrubber (SIR), butadiene-isoprene copolymer rubber, solution-polymerizedrandom styrene-butadiene-isoprene copolymer rubber (SIBR),emulsion-polymerized SIBR, high-vinyl SBR/low-vinyl SBR block copolymerrubber, and block copolymers such aspolystyrene-polybutadiene-polystyrene block copolymers. Among them, NR,BR, IR, SBR and SIBR are preferred. From the viewpoint ofprocessability, NR and IR are particularly preferred.

Diene Rubbers Having a Heteroatom-containing Polar Group

In the present invention, it is preferable to use, as the diene rubbercomponent, a diene rubber having a heteroatom-containing polar group ora combination of a diene rubber having a heteroatom-containing polargroup and another diene rubber, because they can give a highly balancedcombination of properties such as heat build-up, tensile strength,abrasion resistance and processability.

The term “heteroatom” as used herein means an atom of an elementbelonging to the second to fourth periods of the period table and togroup VB or VIB thereof. Specific examples thereof include nitrogen,oxygen, sulfur and phosphorus atoms. Among them, nitrogen and oxygenatoms are preferred.

Polar groups containing such a heteroatom include, for example,hydroxyl, oxy, epoxy, carboxyl, carbonyl, oxycarbonyl, sulfide,disulfide, sulfonyl, sulfinyl, thiocarbonyl, imino, amino, nitrile,ammonium, imido, amido, hydrazo, azo and diazo groups. Among them,hydroxyl, oxy, epoxy, sulfide, disulfide, imino and amino groups arepreferred; hydroxyl, amino and oxy groups are more preferred; andhydroxyl and amino groups are most preferred.

No particular limitation is placed on the type of the diene rubberhaving a heteroatom-containing polar group, provided that it is a dienerubber having, in the molecule, at least one polar group as describedabove. Specifically, the diene rubber having a heteroatom-containingpolar group may comprise, for example, (1) a polar group-containingdiene rubber such as a copolymer formed from a vinyl monomer having aheteroatom-containing polar group and a conjugated diene, or a copolymerformed from a vinyl monomer having a heteroatom-containing polar group,a conjugated diene and an aromatic vinyl, or (2) a polargroup-containing diene rubber obtained by providing a polymer of aconjugated diene which has a combined active metal in the molecule or acopolymer of a conjugated diene and an aromatic vinyl which has acombined active metal in the molecule, and reacting the (co)polymer witha modifying agent to introduce a heteroatom-containing polar group intothe (co)polymer.

In the above-described diene rubber (1) having a heteroatom-containingpolar group which is formed by copolymerization, the contents of variousmonomers may be suitably chosen according to the intended purpose. Inthe case of a copolymer formed from a vinyl monomer having aheteroatom-containing polar group and a conjugated diene, the content ofcombined vinyl monomer units having a heteroatom-containing polar groupis usually in the range of 0.01 to 20% by weight, preferably 0.05 to 15%by weight, and more preferably 0.1 to 10% by weight; and the content ofcombined conjugated diene units is usually in the range of 80 to 99.99%by weight, preferably 85 to 99.95% by weight, and more preferably 90 to99.9% by weight. In order to achieve a highly balanced combination ofheat build-up and wet skid resistance, it is especially preferable touse a copolymer formed from a vinyl monomer having aheteroatom-containing polar group, a conjugated diene and an aromaticvinyl. In such a case, the content of combined vinyl monomer unitshaving a heteroatom-containing polar group is usually in the range of0.01 to 20% by weight, preferably 0.05 to 15% by weight, and morepreferably 0.1 to 10% by weight; the content of combined conjugateddiene units is usually in the range of 40 to 94.99% by weight,preferably 50 to 85% by weight, and more preferably 55 to 80% by weight;and the content of combined aromatic vinyl units is usually in the rangeof 5 to 55% by weight, preferably 10 to 45% by weight, and morepreferably 15 to 40% by weight.

In the above-described polar group-containing diene rubber (2) obtainedby introducing a heteroatom-containing polar group according to themodification method, the contents of various monomers may be suitablychosen according to the desired properties. Specifically, the content ofcombined conjugated diene units is usually in the range of 40 to 100% byweight, preferably 50 to 90% by weight, and more preferably 60 to 85% byweight; and the content of combined aromatic vinyl units is usually inthe range of 0 to 60% by weight, preferably 10 to 50% by weight, andmore preferably 15 to 40% by weight.

Examples of the conjugated diene include 1,3-butadiene,2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene,2-chloro-1,3-butadiene and 1,3-pentadiene. Among them, 1,3-butadiene and2-methyl-1,3-butadiene are preferred, and 1,3-butadiene is morepreferred. These conjugated dienes may be used alone or in admixture oftwo or more.

As the aromatic vinyl, an aromatic vinyl compound not having theabove-described polar group is used. Examples thereof include styrene,α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene,2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene,5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene andmonofluorostyrene. Among them, styrene is preferred. These aromaticvinyls may be used alone or in admixture of two or more.

No particular limitation is placed on the type of the vinyl monomerhaving a heteroatom-containing polar group, provided that it is apolymerizable monomer has at least one polar group in the molecule.Specific examples thereof include amino-containing vinyl monomers,hydroxyl-containing vinyl monomers and oxy-containing vinyl monomers.Among them, hydroxyl-containing vinyl monomers and amino-containingvinyl monomers are preferred. These vinyl monomers having aheteroatom-containing polar group may be used alone or in admixture oftwo or more.

The amino-containing vinyl monomers are polymerizable monomers having,in the molecule, at least one amino group selected from primary,secondary and tertiary amino groups. Among them, tertiaryamino-containing vinyl monomers are particularly preferred.

Examples of the primary amino-containing vinyl monomers includeacrylamide, methacrylamide, p-aminostyrene, aminomethyl (meth)acrylate,aminoethyl (meth)acrylate, aminopropyl (meth)acrylate and aminobutyl(meth)acrylate.

Examples of the secondary amino-containing vinyl monomers includeanilinostyrenes as disclosed in Japanese Patent Laid-Open No.130355/'86: anilinophenylbutadienes as disclosed in Japanese PatentLaid-Open No. 130356/'86; and N-monosubstituted (meth)acrylamides suchas N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide,N-methylolacrylamide and N-(4-anilinophenyl)methacrylamide.

Examples of the tertiary amino-containing vinyl monomers includeN,N-disubstituted aminoalkyl acrylates, N,N-disubstitutedaminoalkylacrylamides, N,N-disubstituted amino aromatic vinyl compoundsand pyridyl-containing vinyl compounds.

Examples of the N,N-disubstituted amino acrylates include acrylic ormethacrylic esters such as N,N-dimethylaminomethyl (meth)acrylate,N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate,N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, N,N-diethylaminobutyl (meth)acrylate,N-methyl-N-ethylaminoethyl (meth)acrylate, N,N-dipropylaminoethyl(meth)acrylate, N,N-dibutylaminoethyl (meth)acrylate,N,N-dibutylaminopropyl (meth)acrylate, N,N-dibutylaminobutyl(meth)acrylate, N,N-dihexylaminoethyl (meth)acrylate,N,N-dioctylaminoethyl (meth)acrylate and acryloylmorpholine. Among them,N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dipropylaminoethyl (meth)acrylate,N,N-dioctylaminoethyl (meth)acrylate and N-methyl-N-ethylaminoethyl(meth)acrylate are preferred.

Examples of the N,N-disubstituted aminoalkyl acrylamides includeacrylamide or methacrylamide compounds such as N,N-dimethylaminomethyl(meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylamide,N,N-dimethylaminopropyl (meth)acrylamide, N,N-dimethylaminobutyl(meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide,N,N-diethylaminopropyl (meth)acrylamide, N,N-diethylaminobutyl(meth)acrylamide, N-methyl-N-ethylaminoethyl (meth)acrylamide,N,N-dipropylaminoethyl(meth)acrylamide, N,N-dibutylaminoethyl(meth)acrylamide, N,N-dibutylaminopropyl (meth)acrylamide,N,N-dibutylamino-butyl (meth)acrylamide, N,N-dihexylaminoethyl(meth)acrylamide, N,N-dihexylaminopropyl (meth)acrylamide andN,N-dioctylaminopropyl (meth)acrylamide. Among them,N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide and N,N-dioctylaminopropyl (meth)acrylamide arepreferred.

Examples of the N,N-disubstituted amino aromatic vinyl compounds includestyrene derivatives such as N,N-dimethylaminoethylstyrene,N,N-diethylaminoethylstyrene, N,N-dipropylaminoethylstyrene andN,N-dioctylaminoethylstyrene.

Examples of the pyridyl-containing vinyl compounds include2-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine and5-ethyl-2-vinylpyridine. Among them, 2-vinylpyridine and 4-vinylpyridineare preferred.

The hydroxyl-containing vinyl monomers are polymerizable monomers havingat least one primary, secondary or tertiary hydroxyl group in themolecule. These hydroxyl-containing vinyl monomers include, for example,hydroxyl-containing unsaturated carboxylic acid monomers,hydroxyl-containing vinyl ether monomer and hydroxyl-containing vinylketone monomers. Among them, hydroxyl-containing unsaturated carboxylicacid monomers are preferred. Examples of the hydroxyl-containingunsaturated carboxylic acid monomers include derivatives (e.g., esters,amides and anhydrides) of acrylic acid, methacrylic acid, itaconic acid,fumaric acid and maleic acid. Among them, ester compounds of acrylicacid and methacrylic acid are preferred.

Specific examples of the hydroxyl-containing vinyl monomers includehydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate,3-chloro-2-hydroxypropyl (meth)acrylate, 3-phenoxy-2-hydroxypropyl(meth)acrylate, glycerol mono(meth)acrylate, hydroxybutyl(meth)acrylate, 2-chloro-3-hydroxypropyl (meth)-acrylate, hydroxyhexyl(meth)acrylate, hydroxyoctyl (meth)acrylate,hydroxymethyl(meth)acrylamide, 2-hydroxypropyl (meth)acrylamide,3-hydroxypropyl (meth)acrylamide, di(ethylene glycol) itaconate,di(propylene glycol) itaconate, bis(2-hydroxypropyl) itaconate,bis(2-hydroxyethyl) itaconate, bis(2-hydroxyethyl) fumarate,bis(2-hydroxyethyl) maleate, 2-hydroxyethyl vinyl ether, hydroxymethylvinyl ketone and allyl alcohol. Among them, hydroxymethyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate,3-phenoxy-2-hydroxypropyl (meth)acrylate, glycerol mono(meth)acrylate,hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl(meth)acrylate, hydroxymethyl(meth)acrylamide,2-hydroxypropyl(meth)acrylamide and 3-hydroxypropyl (meth)acrylamide arepreferred.

Examples of the oxy-containing vinyl monomers include thealkoxysilyl-containing vinyl monomers disclosed in Japanese PatentLaid-Open No. 188356/'95, such as trimethoxyvinylsilane,triethoxyvinylsi lane, 6-trimethoxysilyl-1,2-hexene,p-trimethoxysilylstyrene, 3-trimethoxysilylpropyl methacrylate and3-triethoxysilylpropyl acrylate.

These vinyl monomers having a heteroatom-containing polar group may beused alone or in admixture of two or more.

Although no particular limitation is placed on the process for preparinga diene rubber having a heteroatom-containing polar group according tothe copolymerization method described in (1) above, emulsionpolymerization is usually employed. For purposes of emulsionpolymerization, any common emulsion polymerization process may beemployed. One example thereof comprises emulsifying or dispersingspecified amounts of the aforesaid monomers in an aqueous medium in thepresence of an emulsifying agent and then effecting emulsionpolymerization with the aid of a radical polymerization initiator.

As the emulsifying agent, there may be used, for example, a long-chainfatty acid salt of 10 or more carbon atoms and/or a rosinate. Specificexamples thereof include potassium and sodium salts of capric acid,lauric acid, myristic acid, palmitic acid, oleic acid and stearic acid.

Examples of the radical polymerization initiator include persulfuricacid salts such as ammonium persulfate and potassium persulfate; andredox initiators such as a combination of ammonium persulfate and ferricsulfate, a combination of an organic peroxide and ferric sulfate, and acombination of hydrogen peroxide and ferric sulfate.

Moreover, a chain transfer agent may be added in order to regulate themolecular weight of the copolymer. Usable chain transfer agents include,for example, mercaptans such as t-dodecyl mercaptan and n-dodecylmercaptan, carbon tetrachloride, thioglycollic acid, diterpene,α-methylstyrene dimer, terpinolene and γ-terpinenes.

The temperature for emulsion polymerization may be suitably chosenaccording to the type of the radical polymerization initiator used.However, it is usually in the range of 0 to 100° C. and preferably 0 to60° C. The manner of polymerization may be either continuouspolymerization or batch polymerization.

As the degree of conversion in emulsion polymerization becomes higher,the polymerization mixture tends to undergo gelation. Consequently, thedegree of conversion is preferably controlled so as to be not greaterthan 90%. It is especially preferable to stop the polymerization at adegree of conversion in the range of 50 to 80%. The polymerizationreaction is usually stopped by adding a polymerization stopper to thepolymerization system when a predetermined degree of conversion isreached. Usable polymerization stoppers include, for example, aminecompounds such as diethylhydroxylamine and hydroxylamine, and quinonecompounds such as hydroquinone and benzoquinone, as well as sodiumnitrite and sodium dithiocarbamate.

After the emulsion polymerization reaction is stopped, unreactedmonomers are removed from the resulting polymer latex as required, andthe pH of the latex is adjusted to a predetermined value as required bythe addition of an acid such as nitric acid or sulfuric acid.Thereafter, a coagulant comprising a salt such as sodium chloride,calcium chloride or potassium chloride is added to and mixed with thelatex to coagulate the polymer in the form of crumbs. These crumbs arewashed, dehydrated and then dried with a band dryer or the like. Thus,the desired polar group-containing diene rubber can be obtained.

In order to prepare a diene rubber having a heteroatom-containing polargroup according to the modification method described in (2) above, adiene rubber having a combined active metal in the molecular chain isfirst prepared. Then, a heteroatom-containing polar group is introducedinto this diene rubber by reacting it with a modifying agent.

No particular limitation is placed on the type of the active metal. Forexample, metals capable of anionic polymerization may be used.Specifically, they include, for example, alkali metals such as lithium,sodium, potassium, rubidium and cesium, which are described in JapanesePatent Laid-Open No. 162604/'83, Japanese Patent Laid-Open No.42552/'86, Japanese Patent Publication No. 30841/'93, Japanese PatentLaid-Open No. 297403/'88 and the like; alkaline earth metals such asberyllium, magnesium, calcium, strontium and barium; and lanthanoidseries rare earth metals such as lanthanum and neodymium. Among them,alkali metals and alkaline earth metals are preferred, and alkali metalsare particularly preferred.

The diene rubber having a combined active metal may be prepared bypolymerizing a conjugated diene, or a conjugated diene and an aromaticvinyl, according to a solution polymerization process using an activemetal-based catalyst as the initiator (Japanese Patent Laid-Open No.162604/'83). An alternative method is to prepare a diene rubberaccording to any of various polymerization techniques (such as emulsionpolymerization and solution polymerization) and subsequently add anactive metal to the diene rubber chain (Japanese Patent Laid-Open No.189203/'83). However, the present invention is not limited to thesemethods.

As the active metal-based catalyst (or active metal-containinginitiator), there may be used an organic alkali metal catalyst, anorganic alkaline earth metal catalyst, an organic acid lanthanoid seriesrare earth metal catalyst or the like. Among them, an organic alkalimetal catalyst is preferred.

Examples of the organic alkali metal catalyst include mono-organolithiumcompounds such as n-butyllithium, sec-butyllithium, t-butyllithium,hexyllithium, phenyllithium and stilbene lithium; multifunctionalorganolithium compounds such as dilithiomethane, 1,4-dilithiobutane,1,4-dilithio-2-ethylcyclohexane and 1,3,5-trilithiobenzene; tertiaryamino-containing organolithium compounds as disclosed in Japanese PatentLaid-Open No. 2916/'95 and Japanese Patent Laid-Open No. 53616/'95; andsodium naphthalene and potassium naphthalene. Among them, organolithiumcompounds are preferred and mono-organolithium compounds areparticularly preferred.

Examples of the organic alkaline earth metal catalyst includen-butylmagnesium bromide, n-hexylmagnesium bromide, ethoxycalcium,calcium stearate, t-butoxystrontium, ethoxybarium, isopropoxybarium,phenoxybarium, diethylaminobarium, barium stearate and ethylbarium.

Examples of the organic acid lanthanoid series rare earth metal catalystinclude a complex catalyst composed of neodymiumversaticate/triethylaluminum hydride/ethylaluminum sesquichloride asdescribed in Japanese Patent Publication No. 64444/'88.

These active metal-containing initiators may be used alone or inadmixture of two or more. In the case of solution polymerization(anionic polymerization), the amount of active metal-containinginitiator used may be suitably chosen according to the type of theinitiator or the desired molecular weight of the formed polymer. It isusually in the range of 1 to 20 millimoles, preferably 2 to 15millimoles and more preferably 3 to 10 millimoles per kilogram of theformed diene rubber.

Anionic polymerization using an initiator as described above is carriedout in a hydrocarbon solvent which does not destroy the initiator. Noparticular limitation is placed on the type of the hydrocarbon solvent,and there may be employed any hydrocarbon solvent that is commonly usedfor purposes of anionic polymerization. It may be selected fromwell-known hydrocarbon solvents including, for example, aliphatichydrocarbons such as n-butane, n-pentane, isopentane, n-hexane,n-heptane and isooctane; alicyclic hydrocarbons such as cyclopentane,cyclohexane and methylcyclopentane; and aromatic hydrocarbons such asbenzene and toluene. Among them, N-hexane, cyclohexane and toluene arepreferred. Moreover, unsaturated hydrocarbons having lowpolymerizability, such as 1-butene, cis-2-butene and 2-hexene, may beused as required. These hydrocarbon solvents may be used alone or inadmixture of two or more. The amount of hydrocarbon solvent used isusually such that the monomer concentration is in the range of 1 to 30%by weight.

In the anionic polymerization reaction, a microstructure regulator maybe added for the purpose of regulating the microstructure of thecombined conjugated diene units or the distribution of the aromaticvinyl copolymerized with the conjugated diene in the copolymer chain.Examples of the microstructure regulator include ethers such astetrahydrofuran, diethyl ether, dioxane, ethylene glycol dimethyl ether,ethylene glycol dibutyl ether, diethylene glycol dimethyl ether anddiethylene glycol dibutyl ether; tertiary amine compounds such astetramethylethylenediamine, trimethylamine, triethylamine, pyridine andquinuclidine; alkali metal alkoxide compounds such as potassiumt-pentoxide and potassium t-butoxide; and phosphine compounds such astriphenylphosphine. These microstructure regulators may be used alone orin admixture of two or more. The amount of microstructure regulator usedis usually in the range of 0 to 200 moles per mole of the initiator.

According to any desired polymerization process such as batch orcontinuous process, the anionic polymerization reaction is usuallycarried out at a temperature in the range of −78 to 150° C. Where anaromatic vinyl is copolymerized, in order to improve the randomarrangement of aromatic vinyl units, it is desirable to feed theconjugated diene or a mixture of the conjugated diene and the aromaticvinyl continuously or intermittently to the reaction system so that theproportion of the aromatic vinyl relative to the combined amount of thearomatic vinyl and the conjugated diene present in the polymerizationsystem is within a specific range, as described, for example, inJapanese Patent Laid-Open No. 140211/'84 and Japanese Patent Laid-OpenNo. 143209/'81.

Specific examples of the polymer formed by the anionic polymerizationinclude polybutadiene, polyisoprene, butadiene-isoprene copolymers,styrene-butadiene copolymers, styrene-isoprene copolymers andstyrene-butadiene-isoprene copolymers. Thus, there is obtained aconjugated diene polymer having an active metal attached to an end ofthe polymer chain (hereinafter referred to as the active polymer).

According to the method in which the addition of an active metal iseffected by an after-reaction (i.e., the after-addition reaction of anactive metal), the polymerization reaction is stopped, for example, byadding an equimolar amount of an alcohol (e.g., methanol or isopropanol)to the aforesaid active polymer. Thereafter, an active metal-containinginitiator and, if necessary, the aforesaid microstructure regulator arenewly added and reacted to introduce the active metal. The reactiontemperature is usually in the range of −78 to 150° C. and preferably 20to 100° C., and the reaction time is usually in the range of 0.1 to 24hours and preferably 0.5 to 4 hours. Thus, there is obtained an activepolymer having a combined active metal in the main polymer chain.Similarly, a conjugated diene polymer obtained by another polymerizationtechnique such as emulsion polymerization may be reacted with an activemetal-containing initiator to introduce the active metal into themolecular chain.

No particular limitation is placed on the type of the modifying agent,provided that it can react with the aforesaid active metal to form apolar group as described previously. For example, various modifyingagents disclosed in Japanese Patent Laid-Open No. 191705/'84, JapanesePatent Laid-Open No. 137913/'85, Japanese Patent Laid-Open No.86074/'87, Japanese Patent Laid-Open No. 109801/'87, Japanese PatentLaid-Open No. 149708/'84, Japanese Patent Laid-Open No. 22940/'89 andthe like. Specifically, they include, for example, compounds having, inthe molecule, at least one substituent selected from carbonyl,thiocarbonyl, amino, aziridine and epoxy groups. Moreover, compoundshaving, in the molecule, both a functional group capable of reactingwith the active metal and a polar group as described previously. In suchcompounds, the functional group capable of reacting with the activemetal may be, for example, a carbon-carbon unsaturated group (e.g.,vinyl), a halogen atom or a carbonyl group.

Specific examples of the modifying agent include ketones such asacetone, benzophenone and acetylacetone; esters such as methyl acetate,methyl adipate, methyl methacrylate and ethyl methacrylate; aldehydessuch as benzaldehyde; epoxies; epihalohydrins; carbodiimides; Schiffbases such as N-ethylethylideneimine, N-methylbenzylideneimine,N-hexylcinnamylideneimine, N-decyl-2-ethyl-1,2-diphenylbutylideneimine,N-phenylbenzylideneimine, N-dodecylcyclohexaneimine,N-propyl-2,5-cyclohexanedieneimine and N-methyl-1-naphthaleneimine;cyclic imine compounds having 2 or 3 carbon atoms; compounds havingvinyl and hydroxyl groups in the molecule; compounds having vinyl andamino groups in the molecule; compounds having vinyl and alkoxysilylgroups in the molecule; compounds having a halogen atom and analkoxysilyl group in the molecule; and compounds having carbonyl andamino groups in the molecule. Among them, epoxies, epihalohydrins,carbodiimides, cyclic imine compounds having 2 or 3 carbon atoms,compounds having vinyl and hydroxyl groups in the molecule, compoundshaving vinyl and amino groups in the molecule, compounds having vinyland alkoxysilyl groups in the molecule, compounds having a halogen atomand an alkoxysilyl group in the molecule, and compounds having carbonyland amino groups in the molecule are preferred in order to achieve amore highly balanced combination of heat build-up characteristics andabrasion resistance, and compounds having carbonyl and amino groups inthe molecule are particularly preferred.

Examples of the epoxies include ethylene oxide, propylene oxide,1,2-epoxybutane, 1,2-epoxyisobutane, 2,3-epoxybutane, 1.2-epoxyhexane,1,2-epoxyoctane, 1,2-epoxydecane, 1,2-epoxytetradecane,1,2-epoxyhexadecane, 1,2-epoxyoctadecane, 1,2-epoxyeicosane,1,2-epoxy-2-pentylpropane, 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene,1,2-epoxy-9-decene, 1,2-epoxycyclopenane, 1.2-epoxycyclohexane,1,2-epoxycyclododecane, 1,2-poxyethylbenzene,1,2-epoxy-1-methoxy-2-methylpropane, glycidyl methyl ether, glycidylethyl ether, glycidyl isopropyl ether, glycidyl allyl ether, glycidylphenyl ether, glycidyl butyl ether,2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane and3-glycidyloxypropyltrimethoxysilane. Among them, ethylene oxide,propylene oxide, 1,2-epoxybutane, 1,2-epoxyisobutane, 2,3-epoxybutane,1,2-epoxyhexane, 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, glycidyl methylether, glycidyl ethyl ether, glycidyl isopropyl ether, glycidyl allylether, glycidyl phenyl ether, glycidyl butyl ether and3-glycidyloxypropyltrimethoxysilane are preferred.

Examples of the epihalohydrins are the compounds derived from theaforesaid epoxies by replacing at least one hydrogen atom with a halogenatom. The preferred range thereof is the same as for the aforesaidepoxies. Specific examples thereof include epichlorohydrin,epibromohydrin, epiiodohydrin, 2,3-epoxy-1,1,1-trifluoropropane and1,2-epoxy-1H, 1H, 2H, 3H, 3H-heptadecafluoroundecane. Among them,epichlorohydrin and epibromohydrin are preferred.

Examples of the carbodiimides include dimethylcarbodiimide,diethylcarbodiimide, dipropylcarbodiimide, dibutylcarbodiimide,dihexylcarbodiimide, dicyclohexylcarbodiimide, dibenzylcarbodiimide,diphenylcarbodiimide, methylpropyicarbodiimide,butylcyclohexylcarbodiimide, ethylbenzylcarbodiimide,propylphenylcarbodiimide and phenylbenzylcarbodiimide. Among them,dicyclohexylcarbodiimide and diphenylcarbodiimide are preferred.

Examples of the cyclic imine compounds having 2 or 3 carbon atomsinclude N-unsubstituted aziridine compounds such as ethyleneimine andpropyleneimine; and N-unsubstituted azetidine compounds such astrimethyleneimine.

As examples of the compounds having a vinyl group and a hydroxyl oramino group in the molecule, there may be used compounds such as theaforesaid hydroxyl-containing vinyl monomers and amino-containing vinylmonomers.

Examples of the compounds having a vinyl group or a halogen atom and analkoxysilyl group in the molecule are those disclosed in Japanese PatentLaid-Open No. 188501/'89. Specifically, they include monovinylsilanecompounds such as trimethoxyvinylsilane, triethoxyvinylsilane,triphenoxyvinylsilane and tri (2-methylbutoxy)vinylsilane; andmonohalogenated alkoxysilane compounds such as trimethoxychlorosilane,triethoxychlorosilane, diethoxymethylchlorosilane,triphenoxychlorosilane and diphenoxyphenyliodosilane. These compoundsmay be used alone or in admixture of two or more. However, the amount ofthe compound added must be determined so that the amount of thefunctional group (i.e., the vinyl group or the halogen atom) is equal toor greater than the equivalent amount for the active metal.

In the compounds having carbonyl and amino groups in the molecule, bothgroups may be adjacent to each other or separated from each other.Examples of the compound in which both groups are adjacent to each otherinclude amides, imides, ureas and isocyanuric acids. Such compounds ofcyclic form are preferred, and N-substituted cyclic amides andN-substituted cyclic ureas are more preferred. Examples of the compoundin which both groups are separated from each other include aminoketonesand aminoaldehydes. N-substituted aminoketones and N-substitutedaminoaldehydes are preferred, and N-substituted aminoketones are morepreferred.

Examples of the N-substituted cyclic amides includeN-methyl-β-propiolactam, N-phenyl-β-propiolactam,N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone,N-t-butyl-2-pyrrolidone, N-methyl-5-methyl-2-pyrrolidone,N-methyl-2-piperidone, N-vinyl-2-piperidone, N-phenyl-2-piperidone,N-methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methyl-ω-laurolactamand N-vinyl-ω-laurolactam. Among them, N-methyl-2-pyrrolidone,N-vinyl-2-pyrrolidone, N-phenyl-2-pyrolidone, N-methyl-2-piperidone,N-vinyl-2-piperidone, N-methyl-ε-caprolactam and N-phenyl-ε-caprolactamare preferred.

Examples of the N-substituted cyclic ureas include1,3-dimethylethyleneurea, 1,3-divinylethylene-urea,1,3-diethyl-2-imidazolidinone and 1-methyl-3-ethyl-2-imidazolidinone.Among them, 1,3-dimethylethyl-eneurea and 1,3-divinylethyleneurea arepreferred.

Examples of the N-substituted aminoketones include4-N,N-dimethylaminoacetophenone, 4-N,N-diethyl-aminoacetophenone,1,3-bis(diphenylamino)-2-propanone,1,7-bis(methylethylamino)-4-heptanone, 4-N,N-dimethyl-aminobenzophenone,4-N,N-di-t-butylaminobenzophenone, 4-N,N-diphenylaminobenzophenone,4,4′-bis(dimethylamino)benzophenone, 4,4′-bis(diethylamino)benzophenoneand 4,4′-bis(diphenylamino)benzophenone. Among them,4,4′-bis(dimethylamino)benzophenone, 4,4′-bis(diethylamino)-benzophenoneand 4,4′-bis(diphenylamino)benzophenone are particularly preferred.

Examples of the N-substituted aminoaldehydes include N-substitutedaminoaldehydes such as 4-N,N-dimethylaminobenzaldehyde,4-N,N-diphenylaminobenzaldehyde and 4-N,N-divinylaminobenzaldehyde.

These modifying agents may be used alone or in admixture of two or more.The amount of modifying agent used may be suitably chosen according tothe type of the modifying agent used and the desired properties.However, it is usually used in the range of 0.1 to 50 equivalents,preferably 0.2 to 20 equivalents, and more preferably 0.3 to 10equivalents.

The modification reaction may be effected by bringing the aforesaidactive polymer having a combined active metal in the molecule intocontact with a modifying agent. When the active polymer is prepared byanionic polymerization, the modification reaction is usually carried outby adding a specified amount of a modifying agent to the active polymersolution before stopping the polymerization. Alternatively, it is alsopossible to introduce an active metal into both an end and the mainchain of the polymer and then react the resulting active polymer with amodifying agent. In the modification reaction, the reaction temperatureand the reaction time may be chosen in wide ranges. Generally, thereaction temperature may range from room temperature to 120° C. and thereaction time may range from several seconds to several hours.

Where the modification reaction is carried out by anionic polymerizationas described above, it is possible to regulate the microstructure of thecombined conjugated diene units in the polar group-containing dienerubber obtained by the modification reaction. Although no particularlimitation is placed on the proportion of vinyl linkages (i.e.,1,2-vinyl and 3,4-vinyl linkages) in the combined conjugated dieneunits, it is usually regulated so as to be in the range of 5 to 95%,preferably 20 to 90%, more preferably 30 to 85%, and most preferably 40to 80%. When the proportion of vinyl linkages in the combined conjugateddiene units is within this range, a highly balanced combination ofproperties such as tensile strength and abrasion resistance is achieved.

These diene rubbers (i.e., diene rubbers having a heteroatom-containingpolar group and other diene rubbers) may be used alone or in admixtureof two or more. When such a polar group-containing diene rubber (A) andone or more other diene rubbers (B) are used in admixture, their mixingratio may be suitably chosen according to the intended application andpurpose. However, the weight ratio of (A) to (B) is usually in the rangeof 10:90 to 90:10, preferably 15:85 to 85:15, and more preferably 20:80to 80:20. In such cases, the composition of the diene rubber componentis as follows. For example, when [the polar group-containing dienerubber (A)] and [NR and/or IR] are used in admixture, their weight ratiois preferably in the range of 20:80 to 80:20 and more preferably 30:70to 70:30. For example, when [the polar group-containing diene rubber(A)], [NR and/or IR] and [SBR] are used in admixture, their weight ratiois preferably in the range of 80-20:10-70:10:70.

No particular limitation is placed on the Mooney viscosity (ML₁₊₄, 100°C.) of the diene rubber component used in the present invention.However, it is usually in the range of 10 to 250, preferably 20 to 150,and more preferably 25 to 120. When the Mooney viscosity is within thisrange, a highly balanced combination of properties such as heatbuild-up, abrasion resistance and processability is preferably achieved.The Mooney viscosity (ML₁₊₄, 100° C.) of the diene rubber component mayalso be regulated so as to be within this range, by adding an oil or thelike to form an oil-extended rubber.

Reinforcing Agent

No particular limitation is placed on the type of the reinforcing agent.For example, silica and carbon black may be used.

No particular limitation is placed on the type of silica. Examplesthereof include dry process white carbon, wet process white carbon,colloidal silica, and precipitated silica as disclosed in JapanesePatent Laid-Open No. 62838/'87. Among them, wet process white carbonconsisting essentially of hydrated silica is particularly preferred.These silicas may be used alone or in admixture of two or more.

No particular limitation is placed on the specific surface area ofsilica. However, the specific surface area of silica should usually bein the range of 50 to 400 m²/g, preferably 100 to 250 m²/g, and morepreferably 120 to 190 m²/g, as expressed in terms of a nitrogenadsorption specific surface area (measured by the BET method), becausesufficient improvements in reinforcing power, abrasion resistance andheat build-up are achieved in such a case. The term “nitrogen adsorptionspecific surface area” as used herein refers to a value measured by theBET method according to ASTM D3037-81.

No particular limitation is placed on the type of carbon black. However,usable carbon blacks include furnace black, acetylene black, thermalblack, channel black and graphite. Among them, furnace black isparticularly preferred. Specific examples thereof include products ofvarious grades such as SAF, ISAF, ISAF-HF, ISAF-LS, IISAF-HS, HAF,HAF-HS, HAF-LS and FEF. These carbon blacks may be used alone or inadmixture of two or more.

No particular limitation is placed on the nitrogen adsorption specificsurface area (N₂SA) of carbon black. However, when it is usually in therange of 5 to 200 m²/g, preferably 50 to 150 m²/g, and more preferably80 to 130 m²/g, tensile strength and abrasion resistance are. improvedto a high degree. Moreover, no particular limitation is placed on theDBP adsorption level of carbon black. However, when it is usually in therange of 5 to 300 ml/100 g, preferably 50 to 200 ml/100 g, and morepreferably 80 to 160 ml/100 g, tensile strength and abrasion resistanceare improved to a high degree.

Abrasion resistance can further be improved by using high-structurecarbon black which is disclosed in Japanese Patent Laid-Open No.230290/'93 and characterized by a cetyltrimethylammonium bromide (CTAB)adsorption specific surface area of 110 to 170 m²/g and a DBP (24MD4BP)adsorption level of 110 to 130 ml/100 g after being repeatedlycompressed four times under a pressure of 24,000 psi.

The amount of reinforcing agent used is in the range of 10 to 200 partsby weight, preferably 20 to 150 parts by weight, and more preferably 30to 120 parts by weight, per 100 parts by weight of the rubber component.

In order to accomplish the objects of the present invention to thefullest extent, it is preferable to use, as the reinforcing agent,silica alone or a combination of silica and carbon black. When acombination of silica and carbon black is used, the mixing ratio thereofmay be suitably chosen according to the intended application or purpose.However, the weight ratio of silica to carbon black is usually in therange of 10:90 to 99:1, preferably 30:70 to 95:5, and more preferably50:50 to 90:10.

Silane Coupling Agent

In the present invention, the addition of a silane coupling agent ispreferable because this brings about further improvements in heatbuild-up and abrasion resistance.

No particular limitation is placed on the type of the silane couplingagent. Examples thereof include vinyltrichlorosilane,vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane,N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane andbis[3-(triethoxysilyl)propyl] tetrasulfide, as well as the tetrasulfidesdescribed in Japanese Patent Laid-Open No. 248116/'94, includingγ-trimethoxysilylpropyl dimethylthiocarbamyl tetrasulfide andγ-trimethoxysilylpropyl benzothiazyl tetrasulfide.

These silane coupling agents may be used alone or in admixture of two ormore. The amount of silane coupling agent used is usually in the rangeof 0.1 to 30 parts by weight, preferably 1 to 20 parts by weight, andmore preferably 2 to 10 parts by weight, per 100 parts by weight ofsilica.

Fatty Acid Salt

No particular limitation is placed on the type of the fatty acid salt.However, fatty acid metal salts may usually be used. The fatty acid usedmay be either a saturated fatty acid or an unsaturated fatty acid. Itsnumber of carbon atoms is usually in the range of 1 to 36, preferably 5to 25, and more preferably 10 to 20. Useful fatty acids include, forexample, formic acid, acetic acid, propionic acid, butyric acid, valericacid, octanoic acid, dodecanoic acid, octenoic acid, stearic acid,lauric acid, oleic acid and eicosanoic acid. Among them, octenoic acid,stearic acid, lauric acid, oleic acid and eicosanoic acid are preferred;and stearic acid and lauric acid are particularly preferred. Examples ofmetal salts include alkali metal salts such as lithium, sodium,potassium, rubidium and cesium salts; alkaline earth metal salts such asberyllium, magnesium, calcium, strontium and barium salts; salts ofgroup III metals in the periodic table, such as aluminum salts; salts ofgroup IV metals in the periodic table, such as tin and lead salts; saltsof group V metals in the periodic table, such as antimony and bismuthsalts; and transition metal salts such as titanium, chromium, manganese,iron, cobalt, nickel, copper, zinc, yttrium, silver, cadmium andlanthanum salts. Among them, alkali metal salts, alkaline earth metalsalts and transition metal salts are preferred; and alkali metal saltsand alkaline earth metal salts are particularly preferred.

Specific examples of preferred fatty acid salts include sodium formate,sodium acetate, calcium acetate, zinc acetate, silver acetate, chromiumacetate, cobalt acetate, strontium acetate, iron acetate, copperacetate, lead acetate, nickel acetate, beryllium acetate, manganeseacetate, magnesium propionate, sodium butyrate, calcium valerate, copperoctanoate, potassium octanoate, lithium dodecanoate, lithium octenoate,sodium octenoate, calcium octenoate, barium octenoate, iron octenoate,cobalt octenoate, copper octenoate, zinc octenoate, lithium stearate,sodium stearate, potassium stearate, rubidium stearate, cesium stearate,beryllium stearate, magnesium stearate, calcium stearate, strontiumstearate, barium stearate, lead stearate, chromium stearate, manganesestearate, iron stearate, cobalt stearate, nickel stearate, cadmiumstearate, zinc stearate, lithium laurate, sodium laurate, potassiumlaurate, rubidium laurate, cesium laurate, beryllium laurate, magnesiumlaurate, calcium laurate, strontium laurate, barium laurate, zinclaurate, iron laurate, sodium oleate, potassium oleate, magnesiumoleate, calcium oleate, zinc oleate, sodium eicosanoate and calciumeicosanoate.

Among these fatty acid salts, copper octanoate, potassium octanoate,lithium dodecanoate, lithium octenoate, sodium octenoate, calciumoctenoate, barium octenoate, iron octenoate, cobalt octenoate, copperoctenoate, zinc octenoate, lithium stearate, sodium stearate, potassiumstearate, rubidium stearate, cesium stearate, beryllium stearate,magnesium stearate, calcium stearate, strontium stearate, bariumstearate, lead stearate, chromium stearate, manganese stearate, ironstearate, cobalt stearate, nickel stearate, cadmium stearate, zincstearate, lithium laurate, sodium laurate, potassium laurate, rubidiumlaurate, cesium laurate, beryllium laurate, magnesium laurate, calciumlaurate, strontium laurate, barium laurate, zinc laurate, iron laurate,sodium oleate, potassium oleate, magnesium oleate, calcium oleate, zincoleate, sodium eicosanoate and calcium eicosanoate are preferred; andlithium octenoate, sodium octenoate, calcium octenoate, bariumoctenoate, lithium stearate, sodium stearate, potassium stearate,rubidium stearate, cesium stearate, beryllium stearate, magnesiumstearate, calcium stearate, strontium stearate, barium stearate, lithiumlaurate, sodium laurate, potassium laurate, rubidium laurate, cesiumlaurate, beryllium laurate, magnesium laurate, calcium laurate,strontium laurate, barium laurate, sodium oleate, potassium oleate,magnesium oleate and calcium oleate are particularly preferred.

These fatty acid salts may be used alone or in admixture of two or more.The amount of fatty acid salt used is in the range of 0.1 to 15 parts byweight, preferably 0.5 to 10 parts by weight, and more preferably 1 to 5parts by weight, per 100 parts by weight of the diene rubber component.

Rubber Compositions

In addition to the above-described components, the rubber compositionsof the present invention may contain desired amounts of conventionalcompounding ingredients such as vulcanizing agents, vulcanizationaccelerators, vulcanization activators, antioxidants, activators,plasticizers, lubricants and fillers.

No particular limitation is placed on the type of the vulcanizing agent.Examples thereof include sulfur such as powdered sulfur, precipitatedsulfur, colloidal sulfur, insoluble sulfur and highly dispersiblesulfur; sulfur halides such as sulfur monochloride and sulfurdichloride; organic peroxides such as dicumyl peroxide and di-tert-butylperoxide; quinone dioximes such as p-quinone dioxime andp,p′-dibenzoylquinone dioxime; organic multivalent amine compounds suchas triethylenetetramine, hexamethylenediamine carbamate and4,4′-methylenebis-o-chloroaniline; and alkylphenol resins having amethylol group. Among them, sulfur is preferred, and powdered sulfur isparticularly preferred. These vulcanizing agents may be used alone or inadmixture of two or more.

The amount of vulcanizing agent used is usually in the range of 0.1 to15 parts by weight, preferably 0.3 to 10 parts by weight, and morepreferably 0.5 to 5 parts by weight, per 100 parts by weight of thediene rubber component. When the amount of vulcanizing agent used is inthis range, there can be obtained a vulcanized product which isexcellent not only in tensile strength and abrasion resistance, but alsoin properties such as heat resistance and residual strain.

Examples of the vulcanization accelerators include sulfenamide typevulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, N-t-butyl-2-benzothiazole sulfenamide,N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazolesulfenamide and N,N′-diisopropyl-2-benzothiazole sulfenamide; guanidinetype vulcanization accelerators such as diphenylguanidine,di-o-tolylguanidine and o-tolylbiguanidine; thiourea type vulcanizationaccelerators such as thiocarbanilide, di-o-tolylthiourea,ethylenethiourea, diethylthiourea and trimethylthiourea; thiazole typevulcanization accelerators such as 2-mercaptobenzothiazole,dibenzothiazyl disulfide, 2-mercaptobenzothiazole zinc salt,2-mercaptobenzothiazole sodium salt, 2-mercaptobenzothiazolecyclohexylamine salt and 2-(2,4-dinitrophenylthio)benzothiazole; thiuramtype vulcanization accelerators such as tetramethylthiuram monosulfide,tetramethylthiuram disulfide, tetraethylthiuram disulfide,tetrabutylthiuram disulfide and dipentamethylenethiuram tetrasulfide;dithiocarbamate type vulcanization accelerators such as sodiumdimethyldithiocarbamate, sodium diethyidithiocarbamate, sodiumdi-n-butylthiocarbamate, lead dimethyidithiocarbamate, zincdimethyidithiocarbamate, zinc diethyldithiocarbamate, zincdi-n-butyidithiocarbamate, zinc pentamethylenedithiocarbamate, zincethylphenyldithiocarbamate, tellurium diethyidithiocarbamate, seleniumdimethyldithiocarbamate, selenium diethyidithiocarbamate, copperdimethyidithiocarbamate, iron dimethyidithiocarbamate,diethyldithiocarbamic acid diethylamine salt,pentamethylenedithiocarbamic acid piperidine salt andmethylpentamethylenedithiocarbamic acid pipecoline salt; andxanthogenate type vulcanization accelerators such as sodiumisopropylxanthogenate, zinc isopropylxanthogenate and zincbutylxanthogenate.

These vulcanization accelerators may be used alone or in admixture oftwo or more. However, it is especially preferable to use a vulcanizationaccelerator comprising at least a sulfenamide vulcanization accelerator.The amount of vulcanization accelerator used is usually in the range of0.1 to 15 parts by weight, preferably 0.3 to 10 parts by weight, andmore preferably 0.5 to 5 parts by weight, per 100 parts by weight of thediene rubber component.

No particular limitation is placed on the type of the vulcanizationactivator. For example, higher fatty acids (e.g., stearic acid) and zincoxide may be used. In the case of zinc oxide, it is preferable to usezinc oxide having a particle size of, for example, not greater than 5 μmand hence high surface activity. Specific examples thereof includeactive zinc oxide having a particle size of, for example, 0.05 to 0.2 μmand zinc oxide having a particle size of, for example, 0.3 to 1 μm.Moreover, zinc oxide treated with an amine type dispersing agent orwetting agent may also be used.

These vulcanization activators may be used alone or in admixture of twoor more. The amount of vulcanization activator used may be suitablychosen according to the type of the vulcanization activator. When ahigher fatty acid is used, its amount used is usually in the range of0.05 to 15 parts by weight, preferably 0.1 to 10 parts by weight, andmore preferably 0.5 to 5 parts by weight, per 100 parts by weight of therubber component. When zinc oxide is used, its amount used is usually inthe range of 0.05 to 10 parts by weight, preferably 0.1 to 5 parts byweight, and more preferably 0.5 to 2 parts by weight, per 100 parts byweight of the rubber component. When the amount of zinc oxide used is inthis range, a highly balanced combination of properties such asprocessability, tensile strength and abrasion resistance is achieved.

Examples of other compounding ingredients include coupling agents otherthan silane coupling agents; activators such as diethylene glycol,polyethylene glycol and silicone oil; fillers such as calcium carbonate,talc and clay; process oils; and waxes.

The rubber compositions of the present invention can be obtained bykneading a mixture of various ingredients in the usual manner. Forexample, the rubber compositions can be obtained by mixing the dienerubber component with compounding ingredients other than the vulcanizingagent and the vulcanization accelerator, and then incorporating thevulcanizing agent and the vulcanization accelerator into the resultingmixture. One exemplary procedure using silica as the reinforcing agentis described below.

In order to mix the diene rubber component with compounding ingredientsother than the vulcanizing agent and the vulcanization accelerator, itis preferable to first mix the diene rubber component with at least aportion of silica by means of a mixing machine such as a roll mill or aBanbury mixer, and then mix the resulting mixture with the remainingcompounding ingredients, except the vulcanizing agent and thevulcanization accelerator. This makes it possible to enhance thedispersibility of silica and thereby yield a rubber composition havingmore excellent properties. In this case, silica may be added at a time.However, if a predetermined amount of silica is divided into two or moreportions and added separately, the silica can be easily dispersed andthis makes it easier to mix the silica with the diene rubber component.For example, 10 to 90% of the silica may be added at the first time andthe remainder may be added at the second time or later. The temperatureat which the diene rubber component is mixed with silica is usually inthe range of 80 to 200° C, preferably 100 to 190° C., and morepreferably 140 to 180° C. If this temperature is unduly low, asufficient improvement in abrasion resistance will not be achieved,while it is unduly high, the diene rubber component may undergoyellowing. The mixing time is usually not less than 30 seconds andpreferably in the range of 1 to 30 minutes. After the resulting mixtureis usually cooled to 100° C. or below and preferably to a temperatureranging from room temperature to 80° C., the vulcanizing agent and thevulcanization accelerator are added thereto and kneaded to form a rubbercomposition in accordance with the present invention. Then, thiscomposition may usually be press-cured at a temperature of 120 to 200°C. and preferably 140 to 180° C. to obtain a vulcanized rubber.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is more specifically described with reference tothe following preparation examples, examples and comparative examples.In these examples, all parts and percentages are by weight unlessotherwise stated.

Various properties were measured according to the following methods.

(1) The content of bound styrene in a copolymer was determined accordingto JIS K6383 (the refractive index method).

(2) The content of amino-containing combined monomer units in acopolymer was determined by dissolving the copolymer in tetrahydrofuran,subjecting this solution twice to a reprecipitation/coagulationtreatment with methanol/acetone (50/50% by volume), drying the resultingprecipitate in vacuo, and analyzing it by 500 MHz ¹H-NMR.

(3) Mooney viscosity (ML₁₊₄, 100° C.) was measured according to JISK6301.

(4) As to tensile strength, modulus at 300% stress (in Kgf/cm²) wasmeasured according to JIS K6301.

(5) As to heat build-up, tan δ at 1% torsion, 20 Hz and 60° C. wasmeasured with an RDA-II (manufactured by Rheometrics Co.). This propertywas expressed in terms of an index number (i.e., tan δ 60° C. index).Greater values of this index number indicate more desirable heatbuild-up characteristics.

(6) Abrasion resistance was measured with a pico abrasion testeraccording to ASTM D2228. This property was expressed in terms of anindex number (i.e., abrasion resistance index). Greater values of thisindex number indicate more desirable abrasion resistance.

(7) Processability was evaluated by observing the way of winding aroundthe rolls and rating it on the following basis.

5: The rubber composition winds around the rolls neatly.

4: The rubber composition lifts up slightly.

3: The rubber composition winds around the rolls, but about a half of itlifts up.

2: The rubber composition winds around the rolls, but lifts upfrequently.

1: The rubber composition scarcely winds around the rolls.

PREPARATION EXAMPLES 1-2

A tank fitted with a stirrer was charged with 200 parts of water, 3parts of rosin soap, 0.15 part of t-dodecyl mercaptan, and each of themonomer compositions shown in Table 1. While the temperature of thereactor was maintained at 5° C., polymerization was initiated by theaddition of a radical polymerization initiator comprising 0.1 part ofcumene hydroperoxide, 0.2 part of sodium formaldehyde sulfoxylate and0.01 part of ferric sulfate. When the degree of conversion reached 70%,the reaction was stopped by the addition of diethylhydroxylamine. Then,unreacted monomers were recovered, and a naphthenic oil was mixed in anamount of 37.5 parts by weight per 100 parts by weight of the polymer.The resulting mixture was coagulated with sulfuric acid and sodiumchloride to form crumbs, followed by drying with a crumb dryer. Thus,diene rubber Nos. 1 and 2 were obtained. Properties of these dienepolymers are shown in Table 1.

TABLE 1 Diene rubber No. 1 2 Amount charged (parts) Butadiene 67 55Styrene 32 44 HEMA (*1) 1 — DMAPAA (*2) — 1 Content (wt. %) Styrene 25.136.5 Polar group-containing monomer 1.2 0.5 Process oil (*3) 37.5 —Process oil (*4) — 37.5 Mooney viscosity (ML₁₊₄, 100° C.) 52 52 (*1)Hydroxyethyl methacrylate. (*2) N,N-Dimethylaminopropylacrylamide. (*3)Sunsen 410 (manufactured by Japan Sun Oil Co., Ltd.; a naphthenic oil).(*4) Flex M (manufactured by Fuji Kosan Co., Ltd.; an aromatic oil).

PREPARATION EXAMPLE 3

An autoclave fitted with a stirrer was charged with 8,000 g ofcyclohexane, 400 g of styrene and 800 g of butadiene. Then, 10millimoles of tetramethylethylenediamine (TMEDA) and 10 millimoles ofn-butyllithium were added to initiate polymerization at 40° C. Tenminutes after the start of the polymerization, 800 g of additionalbutadiene was continuously added. After it was confirmed that the degreeof conversion reached 100%, 10 millimoles of N-methyl-ε-caprolactam(NMC) was added and reacted for 20 minutes. After completion of thereaction, 20 millimoles of methanol was added as a stopper. After theaddition of 20 g of 2,6-di-t-butylphenol, the polymer was recovered bysteam stripping. Thus, diene rubber No. 3 was obtained. Properties ofthis polymer are shown in Table 2.

PREPARATION EXAMPLES 4-7

Employing the polymerization conditions shown in Table 2, polymerizationwas carried out in the same manner as in Preparation Example 3.Thereafter, tin tetrachloride (SnCl₄) was added in the amount shown inTable 2 and reacted for 30 minutes. Then, butadiene was added in anamount equal to double the molar amount of n-butyllithium used andreacted for 15 minutes. Subsequently, the modifying agent shown in Table2 was added and reacted for 30 minutes. Thereafter, the polymer wasrecovered in the same manner as in Preparation Example 3. Thus, dienerubber Nos. 4 to 7 were obtained. Properties of these polymers are shownin Table 2.

TABLE 2 Diene rubber No. 3 4 5 6 7 Polymerization conditions Amount ofstyrene charged (g) 800 310 460 400 460 Amount of butadiene charged (g)800 600 700 800 700 Amount of butadiene after-added (g) 400 1090 840 800840 Minimum temperature (° C.) 50 50 50 40 50 Maximum temperature (° C.)80 70 70 60 70 Amount of n-butyllithium (mmol) 10 12 11 10 11 TMEDA(mmol) 20 4.0 3.5 10 3.5 SnCl₄ (mmol) — 1.2 1.1 1.0 1.1 Type ofmodifying agent (*1) NMC EO NVP EAB — Modifying agent (mmol) 10 8 8 8 —Polymer properties Content of bound styrene (wt. %) 40.8 15.6 22.9 20.822.1 Content of 1,2-vinyl (wt. %) 51.0 32.0 33.1 63.1 34.2 Mooneyviscosity (ML₄₊₁, 100° C.) 65 71 70 68 71 (*1) NMC:N-Methyl-ε-caprolactam. EO: Ethylene oxide. NVP: N-vinylpyrrolidone.EAB: 4,4′-Bis(diethylamino)benzophenone.

EXAMPLES 1-8 AND COMPARATIVE EXAMPLE 1

Each of diene rubber Nos. 1 and 2 prepared in the foregoing PreparationExamples and the commercially available diene rubbers shown in Table 4was used as the raw rubber. According to the formulation shown in Table3, all of the raw rubber, half of silica, and half of the silanecoupling agent were mixed at 170° C. for 2 minutes in a Brabender typemixer having a capacity of 250 ml. Then, the remaining compoundingingredients, except sulfur and the vulcanization accelerator, were addedand this mixture was kneaded at the same temperature for 3 minutes. Theamounts of raw rubber, silica, carbon black, silane coupling agent,process oil and fatty acid salt used are shown in Table 4.

Subsequently, the resulting mixture, sulfur and the vulcanizationaccelerator were added to an open roll mill kept at 50° C., and kneadedtherein. Thereafter, specimens were prepared by press curing at 160° C.for 30 minutes and used to measure various properties. The results thusobtained are shown in Table 4.

TABLE 3 First Second Third Formulation 1 time time time Raw rubber All —— Silica Half Half — Carbon black (*1) — All — Silane coupling agent(*2) Half Half — Process Oil (*3) — Variable — Zinc oxide (*4) —Variable — Stearic acid — 2 — Fatty acid salt (*5) — 3 — Wax (*6) — 5 —Antioxidant (*7) — 2 — Sulfur — — 1.5 Vulcanization accelerator (*8) — —3 (*1) Seast KH (manufactured by Tokai Carbon Co., Ltd.). (*2) Si 69(manufactured by Degussa Co.). (*3) Flex M (manufactured by Fuji KosanCo., Ltd.). (*4) Zinc Oxide #1 (manufactured by Honsho Chemical Co.,Ltd.; particle size = 0.4 μm). (*5) Calcium stearate (manufactured byAsahi Denka Kogyo K.K.). (*6) Splendor R-100 (manufactured by KaoCorporation). (*7) Nocrak 6C (manufactured by Oouchi Shinko Co., Ltd.).(*8) Nocceler CZ (manufactured by Oouchi Shinko Co., Ltd.).

TABLE 4 Compara- tive Example Example 1 2 3 4 5 6 7 8 1 Rubber component(parts) (*1) Diene rubber No. 1 137.5 137.5 — — — — — — — (100) (100)Diene rubber No. 2 — — 137.5 137.5 68.75 (100) (100) (50) SBR 1778J (*2)— — — — — 137.5 — 137.5 137.5 (100) (100) (100) SBR 9520 (*3) — — — — —— 137.5 — — (100) IR 2200 (*4) — — — — 50 — — — — Compoundingingredients (parts) Silica (*5) 80 80 80 — 50 80 80 — — Silica (*6) — —— 80 — — — 80 80 Carbon black — — — — 30 — — — — Silane coupling agent 44 4 4 3 4 4 4 4 Process oil — — — — 18.75 — — — — Fatty acid salt 2 4 22 2 2 2 2 — 300% stress (Kgf/cm²) 155 162 142 133 153 135 139 109 80 tanδ 60° C. index (*7) 127 131 133 127 127 119 116 116 100 Abrasionresistance index (*7) 145 156 128 121 138 112 109 107 100 Processability5 5 5 5 5 4 4 4 4 (*1) The value in parentheses is the weight of therubber component freed of oil. (*2) Oil-extended SBR (manufactured byNippon Zeon Co., Ltd.; bound styrene content = 23.5% by weight; Mooneyviscosity (ML₁₊₄, 100° C.) = 42; a naphthenic oil). (*3) Oil-extendedSBR (manufactured by Nippon Zeon Co., Ltd.; bound styrene content = 35%by weight; Mooney viscosity (ML₁₊₄, 100° C.) = 49; an aromatic oil).(*4) High-cis polyisoprene rubber (manufactured by Nippon Zeon Co.,Ltd.; Mooney viscosity (ML₁₊₄, 100° C.) = 83). (*5) Z1165 MP(manufactured by Rhone-Poulenc Co.; nitrogen adsorption specific surfacearea = 175 m²/g). (*6) Nipsil VN3 (manufactured by Nippon Silica Co.,Ltd.; nitrogen adsorption specific surface area = 240 m²/g). (*7) Theseindices are expressed by taking the values of Comparative Example 1 as100.

It can be seen from the results shown in Table 4 that the vulcanizedrubbers obtained from the rubber compositions of the present invention(Examples 1-8) are excellent in all properties including tensilestrength, heat build-up, abrasion resistance and processability.Moreover, it can be seen that, especially when a diene rubber having aheteroatom-containing polar group such as a hydroxyl group or a tertiaryamino group is used as the diene rubber component (Examples 1-5), allproperties including tensile strength, heat build-up, abrasionresistance and processability are highly balanced. Furthermore, it canbe seen that tensile strength, heat build-up and abrasion resistance arefurther improved by using silica having a small specific surface area(by comparison of Examples 3 and 4 or Examples 6 and 8) and thatexcellent heat build-up and abrasion resistance are achieved even by thecombined use of natural rubber and carbon black (Example 5).

EXAMPLES 9-13 AND COMPARATIVE EXAMPLES 2-3

Using each of the raw rubbers shown in Table 6, the following procedurewas performed according to Formulation 2 shown in Table 5. First of all,all of the raw rubber, half of silica, and half of the silane couplingagent were placed in a Banbury mixer having a capacity of 250 ml, andkneaded at 160° C. for 2 minutes. Then, the remaining compoundingingredients, except sulfur and the vulcanization accelerator, were addedand this mixture was kneaded at the same temperature for 2.5 minutes.Subsequently, the resulting mixture, sulfur and the vulcanizationaccelerator were added to an open roll mill kept at 50° C., and kneadedtherein. Thereafter, specimens were prepared by press curing at 160° C.for 30 minutes and used to measure various properties. The results thusobtained are shown in Table 6.

TABLE 5 First Second Third Formulation 2 time time time Raw rubber All —— Silica Half Half — Silane coupling agent (*1) Half Half — Process Oil— Variable — Diethylene glycol — Variable — Zinc oxide (*2) — 2 —Stearic acid — Variable — Fatty acid salt — Variable — Antioxidant (*3)— 2 — Sulfur — — 1.4 Vulcanization accelerator (*4) — — Variable (*1) Si69 (manufactured by Degussa Co.). (*2) Zinc Oxide #1 (manufactured byHonsho Chemical Co., Ltd.). (*3) Nocrak 6C (manufactured by OouchiShinko Co., Ltd.). (*4) Nocceler CZ (manufactured by Oouchi Shinko Co.,Ltd.).

TABLE 6 Comparative Example Example 9 10 11 12 13 2 3 Rubber component(parts) Diene rubber No. 3 70 — — — — — — Diene rubber No. 4 — — — — — —Diene rubber No. 5 — — 100 — — — — Diene rubber No. 6 — 100 — 100 — — —Diene rubber No. 7 — — — — 100 100 100 IR 2200 (*1) 30 — — — — — — —Compounding ingredients (parts) Silica (*2) 40 50 50 — — — — Silica (*3)— — — 50 50 50 50 Carbon black 20 — — — — — — Silane coupling agent 2 34 3 3 3 3 Process oil (*4) 10 — 10 10 20 20 20 Process oil (*5) — 10 — —— — — Fatty acid salt (*6) — 2 2 2 2 — — Fatty acid salt (*7) 2 — — — —— — Stearic acid 2 2 2 2 2 4 2 Vulcanization accelerator 2.5 2 2.5 2 2 22 300% stress (Kgf/cm²) 148 115 128 135 116 90 100 tan δ 60° C. index(*8) 128 136 122 125 107 105 100 Abrasion resistance index (*8) 155 114122 114 104 75 100 Processability 5 4 4 5 4 3 3 (*1) High-cispolyisoprene (manufactured by Nippon Zeon Co., Ltd.). (*2) 1165 MP(manufactured by Rhone-Poulenc Co., nitrogen adsorption specific surfacearea = 175 m²/g). (*3) Nipsil VN3 (manufactured by Nippon Silica Co.,Ltd.; nitrogen adsorption specific surface area = 240 m²/g). (*4)KF-96-200 (manufactured by Shin-etsu Chemical Co., Ltd.; silcone oil).(*5) Flex M (manufactured by Fuji Kosan Co., Ltd.). (*6) Lithiumstearate (manufactured by Sakai Chemical Industry Co., Ltd.). (*7)Calcium laurate (manufactured by Nippon Oil & Fats Co., Ltd.). (*8)These indices are expressed by taking the values of Example 3 as 100.

It can be seen from the results shown in Table 6 that the vulcanizedrubbers obtained from the rubber compositions of the present invention(Examples 9-13) are excellent in all properties including tensilestrength, heat build-up, abrasion resistance and processability.Moreover, it can be seen that, when a diene rubber having aheteroatom-containing polar group introduced thereinto is used as thediene rubber component (Examples 9-12), all properties including tensilestrength, heat build-up, abrasion resistance and processability arehighly balanced. On the other hand, it can be seen that tensile strengthand abrasion resistance are reduced when an increased amount of a fattyacid (e.g., stearic acid) is used in place of the fatty acid salt(Comparative Example 2).

Various embodiments of the present invention are given below.

(1) A rubber composition comprising 100 parts by weight of a dienerubber component, 10 to 200 parts by weight of a reinforcing agent, and0.1 to 15 parts by weight of a fatty acid salt.

(2) A rubber composition as described in (1) wherein the Mooneyviscosity (ML₁₊₄, 100° C.) of the diene rubber component is in the rangeof 10 to 200.

(3) A rubber composition as described in (1) or (2) wherein the dienerubber is at least one member selected from the group consisting ofnatural rubber, polyisoprene rubber, polybutadiene rubber,styrenebutadiene copolymers and styrene-isoprene-butadiene terpolymers.

(4) A rubber composition as described in (1) or (2) wherein the dienerubber comprises a diene rubber having a heteroatom-containing polargroup, or a diene rubber having a heteroatom-containing polar group andanother diene rubber.

(5) A rubber composition as described in (4) wherein the heteroatom isan atom of an element belonging to the second to fourth period of theperiodic table and group VB or VIB thereof.

(6) A rubber composition as described in (5) wherein the heteroatom is anitrogen, oxygen, sulfur or phosphorus atom.

(7) A rubber composition as described in (4) wherein theheteroatom-containing polar group is a hydroxyl, oxy, epoxy, carboxyl,carbonyl, oxycarbonyl, sulfide, disulfide, sulfonyl, sulfinyl,thiocarbonyl, imino, amino, nitrile, ammonium, imido, amido, hydrazo,azo or diazo group.

(8) A rubber composition as described in any of (4) to (7) wherein thediene rubber having a heteroatom-containing polar group is a copolymercontaining units of a polar group-containing vinyl monomer, such as acopolymer formed from a vinyl monomer having a heteroatom-containingpolar group and a conjugated diene, or a copolymer formed from a vinylmonomer having a hetero-atom-containing polar group, a conjugated dieneand an aromatic vinyl.

(9) A rubber composition as described in (8) wherein the diene rubberhaving a heteroatom-containing polar group is a copolymer composed of0.01 to 20% by weight of combined vinyl monomer units having aheteroatom-containing polar group, 40 to 99.99% by weight of combinedconjugated diene units, and 0 to 55% by weight of combined aromaticvinyl units.

(10) A rubber composition as described in (8) or (9) wherein the vinylmonomer having a heteroatom-containing polar group is at least onemember selected from the group consisting of an amino-containing vinylmonomer, a hydroxyl-containing vinyl monomer and an oxy-containing vinylmonomer.

(11) A rubber composition as described in (10) wherein theamino-containing vinyl monomer is a tertiary amino-containing vinylmonomer.

(12) A rubber composition as described in (11) wherein the tertiaryamino-containing vinyl monomer is at least one member selected from thegroup consisting of an N,N-disubstituted aminoalkylate, anN,N-disubstituted aminoalkylacrylamide, an N,N-disubstituted aminoaromatic vinyl compound and a pyridyl-containing vinyl compound.

(13) A rubber composition as described in (10) wherein thehydroxyl-containing vinyl monomer is a hydroxyl-containing unsaturatedcarboxylic acid monomer.

(14) A rubber composition as described in (13) wherein thehydroxyl-containing unsaturated caroxylic acid monomer is ahydroxyl-containing acrylic ester or a hydroxyl-containing methacrylicester.

(15) A rubber composition as described in any of (4) to (7) wherein thediene rubber having a heterotom-containing polar group is a polargroup-containing diene rubber obtained by reacting a modifying agentwith a polymer of a conjugated diene which has a combined active metalin the molecule, or a copolymer of a conjugated diene and an aromaticvinyl which has a combined active metal in the molecule, and therebyintroducing a polar group into the polymer or copolymer.

(16) A rubber composition as described in (15) wherein the diene rubberhaving a heteroatom-containing polar group is a polymer or copolymercomposed of 40 to 100% by weight of combined conjugated diene units and60 to 0% by weight of combined aromatic vinyl units.

(17) A rubber composition as described in (15) or (16) wherein theactive metal is a metal capable of anionic polymerization.

(18) A rubber composition as described in (17) wherein the metal capableof anionic polymerization is an alkali metal.

(19) A rubber composition as described in any of (15) to (18) whereinthe active metal is attached to an end of the polymer chain.

(20) A rubber composition as described in (19) wherein the polymer orcopolymer having an active metal attached to an end of the polymer chainis one obtained by anionic polymerization.

(21) A rubber composition as described in any of (15) to (20) whereinthe modifying agent is at least one member selected from the groupconsisting of ketones, esters, aldehydes, epoxies, epihalohydrins,carbodiimides, Schiff bases and cyclic imine compounds having 2 or 3carbon atoms.

(22) A rubber composition as described in any of (15) to (20) whereinthe modifying agent is a compound having, in the molecule, a functionalgroup reactive with the active metal and a heteroatom-containing polargroup.

(23) A rubber composition as described in (22) wherein the functionalgroup reactive with the active metal is a carbon-carbon unsaturatedgroup, a halogen atom or a carbonyl group.

(24) A rubber composition as described in (23) wherein the carbon-carbonunsaturated group is a vinyl group.

(25) A rubber composition as described in any of (22) to (24) whereinthe heteroatom-containing polar group is a hydroxyl, oxy or amino group.

(26) A rubber composition as described in (22) wherein the compoundhaving a functional group and a polar group in the molecule is acompound having vinyl and hydroxyl groups, a compound having vinyl andamino groups, a compound having vinyl and alkoxysilyl groups, a compoundhaving a halogen atom and an alkoxysilyl group, or a compound havingcarbonyl and amino groups.

(27) A rubber composition as described in any of (15) to (26) wherein,in the diene rubber having a heteroatom-containing polar group, theproportion of vinyl linkages in the combined conjugated diene units isin the range of 10 to 90%.

(28) A rubber composition as described in any of (8) to (27) wherein theconjugated diene is butadiene or isoprene.

(29) A rubber composition as described in any of (8) to (28) wherein thearomatic vinyl is styrene.

(30) A rubber composition as described in any of (1) to (29) wherein thefatty acid salt is a fatty acid metal salt.

(31) A rubber composition as described in (30) wherein the fatty acidmetal salt is at least one member selected from the group consisting ofalkali metal, alkaline earth metal and transition metal salts of fattyacids.

(32) A rubber composition as described in (30) or (31) wherein the fattyacid has 1 to 36 carbon atoms.

(33) A rubber composition as described in any of (1) to (32) wherein thereinforcing agent is carbon black.

(34) A rubber composition as described in any of (1) to (32) wherein thereinforcing agent is silica.

(35) A rubber composition as described in any of (1) to (32) wherein thereinforcing agent comprises carbon black and silica.

(36) A rubber composition as described in (35) wherein silica and carbonblack are used in a weight ratio of 10:90 to 99:1.

(37) A rubber composition as described in any of (34) to (36) whereinthe specific surface area of silica is in the range of 50 to 400 m²/g asexpressed in terms of a nitrogen adsorption specific surface area(measured by the BET method).

(38) A rubber composition as described in any of (1) to (37) whichfurther contains a silane coupling agent.

(39) A rubber composition as described in (38) wherein the silanecoupling agent is used in an amount of 0.1 to 30 parts by weight per 100parts by weight of silica.

(40) A rubber composition as described in any of (1) to (39) whichfurther contains a vulcanizing agent, a vulcanization accelerator and avulcanization activator.

(41) A rubber composition as described in (40) which contains 0.1 to 15parts by weight of the vulcanizing agent and 0.1 to 15 parts by weightof the vulcanization accelerator per 100 parts by weight of the rubbercomponent.

(42) A rubber composition as described in (40) or (41) which contains atleast a sulfenamide type vulcanization accelerator as the vulcanizationaccelerator.

(43) A rubber composition as described in any of (40) to (42) whichcontains zinc oxide as the vulcanization activator.

(44) A rubber composition as described in (43) wherein the particle sizeof zinc oxide is not greater than 5 μm.

(45) A rubber composition as described in (43) or (44) wherein zincoxide is used in an amount of 0.05 to 10 parts by weight per 100 partsby weight of the rubber component.

INDUSTRIAL APPLICABILITY

The compositions of the present invention yield vulcanized rubbersshowing marked improvements in tensile strength and abrasion resistanceand having excellent processability, without detracting from excellentrolling resistance characteristic of silica-filled materials. Theserubber compositions can be used in various applications by making themost of such properties. For example, they can be used as materials forforming various parts of tires, such as tread, carcass, sidewalls andbeads; for rubber products such as hoses, window frames, belts, shoesoles, rubber vibration isolators and automobile parts; and asreinforcing rubbers for resins such as impact-resistant polystyrene andABS resin. In particular, they can be expected to be highly useful forthe tire treads of, for example, low-fuel-consumption tires, all-seasontires, high-performance tires and studless tires.

What is claimed is:
 1. A rubber composition comprising 100 parts byweight of a diene rubber component, 10 to 200 parts by weight of areinforcing agent comprising silica alone or a combination of silica andcarbon black, the weight ratio of silica to carbon black being in therange of 50:50 to 90:10, and 0.1 to 15 parts by weight of an alkalimetal salt or an alkaline earth metal salt of a fatty acid having 5 to25 carbon atoms, and a silane coupling agent in an amount of 0.1 to 30parts per 100 parts by weight of silica.
 2. A rubber composition asclaimed in claim 1, wherein the Mooney viscosity (ML₁₊₄, 100° C.) of thediene rubber component is in the range of 10 to
 200. 3. A rubbercomposition as claimed in claim 1, wherein the diene rubber is at leastone member selected from the group consisting of natural rubber,polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymersand styrene-isoprene-butadiene terpolymers.
 4. A rubber composition asclaimed in claim 1, wherein the diene rubber comprises a diene rubberhaving a heteroatom-containing polar group, or such a polargroup-containing diene rubber and another diene rubber.
 5. A rubbercomposition as claimed in claim 4, wherein the weight ratio of the dienerubber having a heteroatom-containing polar group to the other dienerubber ranges from 10:90 to 90:10.
 6. A rubber composition as claimed inclaim 4, wherein the other diene rubber is at least one member selectedfrom the group consisting of natural rubber, polyisoprene rubber,polybutadiene rubber, styrene-butadiene copolymers andstyrene-isoprene-butadiene terpolymers.
 7. A rubber composition asclaimed in claim 4, wherein the diene rubber having aheteroatom-containing polar group is a copolymer formed from a vinylmonomer having a heteroatom-containing polar group and a conjugateddiene, or a copolymer formed from a vinyl monomer having aheteroatom-containing polar group, a conjugated diene and an aromaticvinyl.
 8. A rubber composition as claimed in claim 7, wherein, in thediene rubber having a heteroatom-containing polar group, the vinylmonomer having a heteroatom-containing polar group is present in aproportion of 0.01 to 20% by weight.
 9. A rubber composition as claimedin claim 7, wherein the diene rubber having a heteroatom-containingpolar group is a copolymer composed of 0.01 to 20% by weight of combinedvinyl monomer units having a heteroatom-containing polar group, 40 to99.99% by weight of combined conjugated diene units, and 0 to 55% byweight of combined aromatic vinyl units.
 10. A rubber composition asclaimed in claim 4, wherein the diene rubber having aheteroatom-containing polar group is a polar group-containing dienerubber obtained by reacting a modifying agent with a polymer of aconjugated diene which has a combined active metal in the molecule, or acopolymer of a conjugated diene and an aromatic vinyl which has acombined active metal in the molecule, and thereby introducing a polargroup into the polymer or copolymer.
 11. A rubber composition as claimedin claim 10, wherein the diene rubber having a heteroatom-containingpolar group is a polymer or copolymer composed of 40 to 100% by weightof combined conjugated diene units and 60 to 0% by weight of combinedaromatic vinyl units.
 12. A rubber composition as claimed in claim 10,wherein the heteroatom-containing polar group is a hydroxyl, oxy, epoxy,carboxyl, carbonyl, oxycarbonyl, sulfide, disulfide, sulfonyl, sulfinyl,thiocarbonyl, imino, amino, nitrile, ammonium, imido, amido, hydrazo,azo or diazo group.
 13. A rubber composition as claimed in claim 4,wherein the heteroatom is a nitrogen, oxygen, sulfur or phosphorus atom.14. A rubber composition as claimed in claim 4, wherein theheteroatom-containing polar group is a hydroxyl, oxy, epoxy, sulfide,imino or amino group.
 15. A rubber composition as claimed in claim 1,wherein the fatty acid metal salt is an alkali metal or alkaline earthmetal salt of a fatty acid having 10 to 20 carbon atoms.
 16. A rubbercomposition comprising 100 parts by weight of a diene rubber component,30 to 120 parts by weight of a reinforcing agent comprising silica aloneor a combination of silica and carbon black, the weight ratio of silicato carbon black being in the range of 50:50 to 90:10, and 1 to 5 partsby weight alkali metal salt or an alkaline earth metal salt of a fattyacid having 10 to 20 carbon atoms, and a silane coupling agent in anamount of 2 to 20 parts per 100 parts by weight of silica.
 17. A rubbercomposition as claimed in claim 16, wherein the diene rubber is at leastone member selected from the group consisting of natural rubber,polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymersand styrene-isoprene-butadiene terpolymers.
 18. A rubber compositionconsisting essentially of 100 parts by weight of a diene rubbercomponent, 30 to 120 parts by weight of a reinforcing agent comprisingsilica alone or a combination of silica and carbon black, the weightratio of silica to carbon black being in the range of 50:50 to 90:10,and 1 to 5 parts by weight alkali metal salt or an alkaline earth metalsalt of a fatty acid having 10 to 20 carbon atoms, and a silane couplingagent, which is a member selected from the group consisting ofvinyltrichlorosilane, vinyltriethoxysilane,vinyltris-(β-methoxyethoxy)silane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane andγ-glycidoxy-propyltrimethoxysilane, in an amount of 2 to 20 parts per100 parts by weight of silica.
 19. A rubber composition as claimed inclaim 18, wherein the diene rubber is at least one member selected fromthe group consisting of natural rubber, polyisoprene rubber,polybutadiene rubber, styrene-butadiene copolymers andstyrene-isoprene-butadiene terpolymers.
 20. A process for preparing therubber composition of claim 1 by adding silica and other ingredients tothe diene rubber component and kneading, which process comprisesdividing a predetermined amount of silica into two or more portions, andadding the two or more portions separately.
 21. A process for preparingthe rubber composition of claim 16 by adding silica and otheringredients to the diene rubber component and kneading, which processcomprises dividing a predetermined amount of silica into two or moreportions, and adding the two or more portions separately.